Supercritical fluid extraction processes are widely used in the food, pharmaceutical, and chemical industries to separate specific components from feedstock materials. These processes are used for the purification of feedstock materials, wherein the removed components are undesirable contaminants, and also for the extraction and recovery of specific components as valuable final products. Supercritical fluids also are used for the cleaning of manufactured parts and fabrics as an alternative to the use of chlorinated solvents.
The cleaning of semiconductor components using supercritical fluids to remove contaminants is a new and rapidly-developing application of this technology in the electronics industry. The use of supercritical fluids in etching and deposition processes, wherein the supercritical fluids serve as carriers of reactant materials, also is developing rapidly in the industry. The supercritical fluids used in these processes must have an extremely high level of purity to avoid residual contamination of semiconductor substrates by particulates, films, or undesirable components that cause short circuits, open circuits, silicon crystal stacking faults, and other defects. These defects result in significant yield reductions and increases in processing costs in the manufacture of microelectronic components. Any significant amount of particulate or molecular contaminants in the supercritical fluid can contaminate semiconductor substrate surfaces and reduce microchip yield to uneconomical levels.
Supercritical fluids for use in these applications typically are prepared by the use of mechanical compressors or pumps to generate the high pressures needed to reach the supercritical region. The most reliable of these mechanical compressors or pumps use pistons with compression seals to separate the pressurized fluid from the hydraulic and lubricating fluids used in compressor operation. Such seals may leak due to wear or other mechanical failure and thereby contaminate the fluids being pressurized. Alternative compressor designs use an oscillating metal diaphragm to separate the pressurized fluid from a hydraulic fluid. However, the diaphragms of such compressors are prone to fatigue failure and require frequent maintenance. Fatigue failure of the diaphragm in such compressors will contaminate the fluid being pressurized.
It is desirable to produce dense fluids, including supercritical fluids, of extremely high purity for applications in microelectronics manufacturing without the use of mechanical pumps or compressors. The present invention, which is described below and defined by the claims which follow, provides an alternative method to produce extremely high purity dense fluids for these applications.